Medicine

Medicine (Latin medicus, “physician”), the science and art of diagnosing, treating, and preventing disease and injury. Its goals are to help people live longer, happier, more active lives with less suffering and disability. Medicine goes beyond the bedside of patients. Medical scientists engage in a constant search for new drugs, effective treatments, and more advanced technology. In addition, medicine is a business. It is part of the health care industry, one of the largest industries in the United States, and among the leading employers in most communities.

Disease has been one of humanity's greatest enemies. Only during the last 100 years has medicine developed weapons to fight disease effectively. Vaccines, better drugs and surgical procedures, new instruments, and understanding of sanitation and nutrition have had a huge impact on human well-being. Like detectives, physicians and other health care professionals use clues to identify, or diagnose, a specific disease or injury. They check the patient's medical history for past symptoms or diseases, perform a physical examination, and check the results of various tests. After making a diagnosis, physicians pick the best treatment. Some treatments cure a disease. Others are palliative—that is, they relieve symptoms but do not reverse the underlying disease. Sometimes no treatment is needed because the disease will get better by itself.

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Steroids

Steroids, large group of naturally occurring and synthetic lipids, or fat-soluble chemicals, with a great diversity of physiological activity. Included among the steroids are certain alcohols (sterols), bile acids, many important hormones, some natural drugs, and the poisons found in the skin of some toads (see Digitalis; Hormone). Various sterols found in the skin of human beings are transformed into vitamin D when they are exposed to the ultraviolet rays of the sun (see Vitamin: Vitamin D). Cholesterol, a major contributor to arteriosclerosis, is a sterol. Steroid hormones, which are similar to but not identical with sterols, include the adrenal cortical steroids hydrocortisone, cortisone, aldosterone, and progesterone; and the female and male sex hormones (see Estrogen; Testosterone). Most oral contraceptives are synthetic steroids consisting of female sex hormones that inhibit ovulation (see Birth Control). Perhaps the most widely used steroids in medicine are cortisone and various synthetic derivatives of this substance. Such steroids are prescription drugs used for a variety of skin ailments, rheumatoid arthritis, asthma and allergies, and various eye diseases, and in cases of adrenal insufficiency, or the malfunctioning of the adrenal cortex (see Adrenal Gland; Endocrine System).

Lipids

Lipids, diverse group of fatty substances found in all living organisms. Lipids are distinguished from other classes of organic compounds in that they do not dissolve in water but are soluble in alcohol, ether, or other organic solvents.

Among the most important lipids are the phospholipids, which are major components of the cell membrane. Phospholipids limit the passage of water and water-soluble compounds through the membrane, enabling the cell to keep its contents separate from the outside environment.

Fats and oils, which are composed of triglycerides, serve as stored energy reserves in plant and animal cells. Each triglyceride is composed of three fatty acid molecules bonded to one glycerol molecule. When an organism has excess energy available from food or from photosynthesis, it may use that energy to form stores of triglycerides. These can later be broken down to yield energy when the organism needs it. Fats and oils contain twice as much stored energy, per unit of weight, as carbohydrates or proteins.

Other important lipids are the waxes, which form protective coatings on the leaves of plants and the skins of animals, and the steroids, which include vitamin D and several key hormones.

Antibodies

Antibody, any of perhaps a million kinds of normally occurring protein molecules that are produced in the body of cells called lymphocytes and that act primarily as a defense against invasion by foreign substances. An important component of the immune system, antibodies are found in the blood of all vertebrates, in the fraction of the blood called gamma globulin.

The synthesis, or manufacture, of antibodies is initiated when a foreign substance, referred to as an antigen, enters the body. Lymphocyte cells respond to the foreign substance by making an antibody with a molecular arrangement that fits the shape of molecules on the surface of the substance so that the antibody combines with it. Common antigens are the protein components of bacteria and viruses. These antigens may enter the body during infection or may be deliberately introduced by vaccination (see Immunization) in order to stimulate the production of antibodies. The binding of antibodies to the surfaces of bacteria, viruses, or toxins (see Toxin) can neutralize and eliminate these harmful substances in any or all of three ways: (1) by directly inactivating them, (2) by enabling other blood cells to engulf and destroy them (see Phagocytosis), and/or (3) by weakening their surfaces and rendering them vulnerable to destruction by other blood proteins (collectively called complement). Animals do not have antibodies to substances to which they have not been exposed, but one animal is able to produce enough different kinds of antibodies to fit the molecular arrangement of any foreign substance it is likely to encounter.

In diseases such as multiple sclerosis and systemic lupus erythematosus, the body mistakenly makes antibodies against normal tissue components (see Autoimmune Diseases). Sometimes viruses may disturb the immune mechanism.

Deficiency Diseases

Deficiency diseases result from insufficient amounts of various healthful nutrients in the diet. Examples include scurvy, caused by a deficiency of vitamin C, or ascorbic acid; pellagra, caused by a deficiency of niacin; and osteoporosis, caused at least in part by a lack of calcium. Deficiency diseases are most prevalent in poverty- or war-stricken areas of the world, where malnutrition is widespread. Deficiency diseases are also found in more affluent nations where food is prevalent but people’s food choices or behavior do not provide well-rounded nutrition, resulting in such disorders as anorexia nervosa, bulimia, and anemia.